1. Field of the Invention
The present invention relates to a function of a substrate transfer robot for avoiding interference within the range of motion thereof, the substrate transfer robot being used for a manufacturing apparatus or a testing apparatus for semiconductor devices or liquid crystal display devices.
2. Description of the Related Art
Substrate transfer robots have been used for manufacturing apparatuses and testing apparatuses for semiconductor devices and liquid crystal display devices (hereinafter referred to as semiconductor manufacturing apparatuses) in order to transfer substrates such as semiconductor wafers, masks, and liquid crystal glass to predetermined positions.
Such substrate transfer robots are capable of transferring substrates to taught positions that have been taught beforehand. A substrate transfer robot can move to a target position with the smallest distance and in the shortest time by moving in a straight line connecting a starting position and the target position of the movement. However, because semiconductor manufacturing apparatuses have been made smaller so as to save space, the range of motion of a substrate transfer robot has become limited. Thus, when an obstacle is disposed in the range of motion, the substrate transfer robot may not be able to move in a straight line.
Against such a background, for example, an apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2000-174092 avoids interference by setting an interference region representing an obstacle in the range of motion of the substrate transfer robot and by generating a path that avoids the interference region if the substrate transfer robot is to make a movement that might pass through the interference region.
The apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2000-174092 avoids interference approximately in the following manner. First, region critical points (vertices) between an interference region and a non-interference region are set, and a plurality of zones are generated using the region critical points. Next, the equation of a straight line that connects the starting position and the target position of a movement is calculated. By comparing the equation of the straight line and the region critical points in zones including the starting position and the target position, whether the straight line interferes with the interference region (whether the line passes through the interference region) is determined. If there be an interference, a path that goes through vicinities of the region critical points is generated so as to avoid interference.
However, the interference avoidance process of Japanese Unexamined Patent Application Publication No. 2000-174092 has the following problem. In determining whether the straight line connecting the starting position and the target position interferes with the interference region, region critical points that exist between the zones including the starting position and the target position are extracted and the coordinates of the region critical points are compared with the equation of the straight line. Therefore, when a large number of region critical points are extracted, the determination becomes complex and time consuming.
Moreover, in most cases, a substrate transfer robot requires a larger range of motion when a hand of the robot holds a substrate than when the robot does not hold a substrate. However, the interference avoidance process according to Japanese Unexamined Patent Application Publication No. 2000-174092 generates an interference avoidance path irrespective of whether the hand holds a substrate. Therefore, a path generated by the process may not be the shortest path between the two points, which does not enable the substrate transfer robot to move between the points within the shortest time.